1. Field of the Invention
This invention relates generally to storing data on an optical disc, and more particularly to a wobble detection circuit, including such a circuit for use in video disc recording media employing Binary Phase Shift Keying (BPSK).
2. Description of the Related Art
Certain optical disc standards, such as HD DVD and DVD+(R and RW), employ BPSK to encode address or location data in the form of bits 0 and 1 on a wobble of an optical disc. During mastering or recording of a disc, this addressing data may be stored as phase modulated data, which is known in the art as Address-in-Pregroove (ADIP). The wobble is a continuous sinusoidal deviation of a track from an average centerline. A wobble signal also may be read from the wobble by a recording drive to precisely rotate the disc according to the frequency of the wobble signal. Using the frequency of the wobble signal, a timing signal may be generated to be used when writing data to the disc. An exemplary embodiment of a disc using BPSK encoding may have data bit 0 represented by a wobble with a first phase (i.e., a normal phase) and data bit 1 represented by a wobble with a second phase 180 degrees apart from the first phase (i.e., an inverted phase). During the mastering process, phase change transitions from a wobble having a normal phase to a wobble having an inverted phase may not be perfect. The inverted phase may extend to its neighboring normal phase wobble or vice versa.
FIG. 1 illustrates an example of a phase change transition problem using a captured HD DVD wobble signal waveform. FIG. 1 shows a captured wobble signal 110 in relation to a wobble clock signal 105. Four arrows 115, 120, 125, 130 point to imperfect phase change transitions from a wobble signal with a normal phase to a wobble signal with an inverted phase. The imperfect phase transitions degrade the performance of wobble signal detection, thereby hampering detection of addressing or ADIP data stored on the wobble of the disc.
Therefore, it would be desirable to have an apparatus that can detect and correct phase transition imperfections associated with optical disc wobble, particularly optical discs storing signals using BPSK.